Agriculture’s Clean Water Alliance (ACWA), a group of 16 ag retailers organized to reduce nutrient loss from farm fields in the Raccoon River and Des Moines River watersheds, is supporting a tile line bioreactor pilot project in the Raccoon River watershed in 2008.
The initial bioreactors to be installed by ACWA will be placed in the West Buttrick Creek/Hardin Creek areas of Greene county. Greene county district conservationist Kevin Kordick is interested in working with ACWA, and there are several farmers who are willing to demonstrate the practice.
The project is being conducted in collaboration with ACWA’s farming partners and an emerging partnership with USDA, soil and water conservation districts, the National Soil Tilth Laboratory, Agri Drain, and the Ag Drainage Management Coalition.
Nitrogen is highly water-soluble, so as water moves off the farm landscape, it carries nitrogen with it. There are practices that capture and filter water at the surface (such as wetlands and retention ponds) but they can be costly and require land to be taken out of production. One alternative filtration practice gaining interest is bioreactors.
Bioreactors are essentially underground trenches filled with a carbon source (commonly wood chips), through which tile water is allowed to flow. The carbon source provides material within which microorganisms can colonize. Using the wood chips as a food source, the microorganisms begin breaking down the nitrate through a denitrification process, and expel the nitrate as a gas.
The systems are easy to construct, relatively inexpensive, take little or no land out of production and are believed to require little maintenance. There are no adverse effects on crop production, and they can be designed to not restrict drainage. And early research has found nitrate removal efficiency averaging between 25 to 35 percent.
Dr Richard Cooke, associate professor of agriculture engineering at the University of Illinois, is a leading researcher of bioreactors. Dr Cooke says the systems work, but “we don’t completely know how.” The bioreactor system, although effective, is not fully understood. “The identity and community dynamics of microorganisms participating in denitrification in tile drain bioreactors are unknown, apart from our findings that both bacterial and fungal species are important to the process. We surmise that the fungi break the cellulose in the wood into smaller organic molecules, which the bacteria then use in their metabolic processes,” Cook said.
ACWA is looking at specific installation sites using GIS and aerial imagery. Once installed, the units will be tested for effectiveness. ACWA will observe nitrate levels in its water monitoring network above and below each site to evaluate the performance. If the bioreactors are proven as a practice in the Raccoon River watershed, they could become one of several integrated solutions for improved water quality.
